Just wanted to add some other information about over wintering bananas. The link below shows how foam insulation can be used to make a banana hut. The designer keeps empty space around the pstems rather than stuffing leaves/straw right up against the pstem. This should reduce mold growth and allow more heat from the ground to travel up the pstem and keep it 'warmer'.
Some year if I have pstems of almost equal size, I'll cover both with a pile of leaves but allow some empty space around the pstem on one of the two.
Something to think about.....
Erik
Link is here:
Permanent banana shelter for winter and spring